Helical slot scanner



Feb. 23, 1954 A, s, DUNBAR 2,670,436

HELICAL SLOT SCANNER Filed May 5, 1950 2 Sheets-Sheet 1 H v INVENTOR ALLEN s. DUNBAR WI ATTORNEYS Feb. 23, 1954 A. s. DUNBAR HELICAL SLOT SCANNER Filed May 3, 1950 2 Sheets-Sheet 2 INVENTOR ALLEN S. DU N BAR BY 5? M2 ATTORNEY? Patented Feb. 23, 1954 um'rso PAT E'NT JIELIOAL SLOT'SCANNER -Alle'n SSD'uiibar, Los'Altos, Calif. sApplicatioli May 3, 1950;'Serial No. 159,801

' Claims.

(Grantedtunderl-T itle 35,11. strode (1952'),

netic lens in a manner such thatth point from whieh the energylis. radiatdcrnove's along a straight line.

In angle tracking radar...systems andithe like, the speed at which'theantenna-can scanai'given this. mafia hasbeen found necessary to reduce the inertia of -the moving partsof the antenna by keepingthe relatively large roccsing-:.apparatus stationary, and by moving ofnlyfthef' pointirro'm which the feeding means radiatselectioinagnetic LEIIBIBY toward itheTfocu'si'ng apparatus. so doing, a' beam results which ineffe'ct quickly scans a given predetermined angle just as if the focusing device and'feeding'in'eans were being moved together as a unit.

In general it is""de'siratile to*-navet tne+rate of scan :not only oftalhighevalue, but substantially uniform as w'ell. .T' Infthe prior art 'ide'v'ices; "this was generally not readily. possible;

-Accordingly, a principal object of the" inven-.

tion is to--provide.i electromagnetic wave propagating apparatus whereini the point froni which the electromagnetic energy emanates :moves 'yquickly and at a-substantially. uniform" rate.

- :Another obj ect of" Ithe v invention is to .zprovide l electromagnetic :wave propagating apparatus wherein the point from which iithe electromagnetic energy emanates. moves quickly along a :astraight line.

:"Fig. 1 isa perspective viewof the propagating apparatus which is the preferred embodiment of t the .1 invention.

2 vislan. overhead view of the embodiment of Fig. 1.

Riga 31s" a cross-sectional .view. ofFigi -z' aiongz sectionline 3-;3.

Fig 4 is .a perspective view of another embodi- Qmentof-Lthe. invention.

5 is aperspective' view or still another em- -bodinient of the invention shownlin'simplifie'd,

of "the" present invention,

-2 4 Basically the present inventionconsists of a waveguide 2 (these reference: characters refer generally to all the figures) located within-la -ho1lowright circular. cylinder lwherel-vonewof 5 .these last two mentioned membershas. i allong,

- narrow-opening or slot 1 and the other member has a helical slot or opening- 6. The wallunem- :bers. having the slots are in contiguous (butnot contact) relation. so that at thevpoint awhere the-openings Band 1 cross each otherla rad-iat- -1ngaperture 8.is formed. The member containing the helical slot or --opening it is caused-etc rotate by means of a suitabledrivingmechanism -l3, the radiating aperture a formed-'atethe-Juncz -predeterminedlareaaisofgreatlimportance. To 1 tion oflthevhelical slot 6 and the straight lslotl --will move atv a predetermined rate untilit reaches atheend of thestraight: slot whereupom -itlwill reappear at theopposite. lend ofethe straight slot and thenbegin to repeat thesame motion. JIo prevent a substantial interruptiontof theiflow of energy through radiating aperture. 8 =lwhen=+the V aperture hasgraisedto the endoi the straightslot -1-thel l-helical slotis made to extendroven substantially a 360 degree surface of the cylinder in which it is formed.

:tDueto the fact that ltherer-is a space or -gap hi l-betweenthefiwave guide 2 andtheouter-pylinder l choke-meansllater described-must be -pro- 1 vided to eifectivelywpreventenergy from (leak- -ing from the slot 'Lof thetwave guide lintothis .ppenihg.

vThe dimensions of Ithe: radiating apertur I 8 appreciably effects the amount of energy which .Lis coupled from the waveguide 2; .Generallyit-he 35,periphery.of-Qthecaperture 8gsho'uld be. .inl.the vicinity of one (orla multipleithereof) Lrree space wavelength. .The shape of theo'peiiing isnot ..critical, however, resonance being the important objective. With such anopeningghowevr, only 40 about .M of the incident, power could be extracted ifrom'the wave guide 2. It was f'o'un'dthat'by-adding a helical channel 5 tol'the' inner surface of cylinder l adjacent the helical sloti or opehmg T61(se Figs. l'3), over 90 percent 'of'theincidefit power could. be extracted; by the'" propagating opening 8 3: over: its "entire' range pfnibvefrjiht. "With" such a modification the dimensions of; the radiating aperture 8 were modified to give'best "results The effect of such a" helical ehanfierwas to shunt the wave, guide 2- adjacen the moving aperture 8 with a' zero impedance reasse smstantially all of the incident energywe'i'it oiit --oraperture 8' rather than 50' percents veident energy continuing downithe' I shunting means a-isehas the a'dvafistage-6r making the anio'untof energy emanation the aperture 8 substantially independent of its position. This is because the portion of the wave guide 2 starting from the helical channel and extending to the end of the wave guide 2 remote from the end of the wave guide 2 which conducts the incident wave to the radiating aperture 8, is effectively shunted out of the circuit. It should be clear that the helical channel is not very readily applicable to the embodiments of Figs. 4 and 5 where the helical slot 6 is not located on the outer cylinder I. Of course, in the embodiment of Fig. 5, the helical slot 6 could be placed in the outer cylinder I instead of on wave guide 2" and thus make the addition of a helical channel readily practicable.

Since rectangular wave guides are more practicable, and because of the increased output possible with the helical channel 5, Fig. l is the preferred embodiment of the invention.

Referring more particularly to Figs. 1-3, the outer cylinder I has a narrow helical slot or opening 6. Within the cylinder I is located a rectangular wave guide 2 with a long, relatively straight and narrow slot or opening I. The slot I is placed in the narrow side of the wave guide 2 and is parallel to the axis of the wave guide 2. The slot I could be placed on the wide side of wave guide 2, but only with added difficulty and complications. The overlapping slots 5 and I should be contiguous to each other and because this is more readily possible with slot 1 cut in the narrow side of wave guide 2, and because energy is more readily coupled out of the narrow side of the wave guide by such a slot, the slot position as shown in Fig. 1 is the preferred one. Of course, slot I need not be parallel to the axis of wave guide 2, but for purposes of obtaining more even power transfer from the moving, propagating opening 8, such a parallel relationship is preferred.

,The axis of waveguide 2 is shown parallel to the axis of cylinder I since this allows the overlapping slots to be more closely adjacent each other. As seen more clearly in Fig. 2, wave guide 2 is not in contact with the cylinder l since cylinder I is to be rotated. Rotation is accomplished by means of a gear means I 2 which. in turn is rotated by a motor 13. When cylinder I is rotated it can be seen that radiating aperture 8 moves from one end of slot I to the other and then suddenly appears at the end of slots I from which it originated. If motor I3 revolves at a uniform rate, thenpropagatirrg opening 8 moves at a uniform rate also. Because of the fact that opening 8 always moves in the same direction, the beam which isv obtained when the opening is directed toward a focusing device will sweep by a given target at asubstantially constant rate.

Since wave guide 2 is not in direct and close contact with the cylinder I, unless choke means .3 vare provided which will effectively close or block off this gap II, appreciable energy will leak from wave guide 2 through slot I into, the inner portion of cylinder I and thus be wasted in addition to causingundesirable effects on the field distribution in wave guide 2. Choke 3 consists of a pair of solid metallic bars each located on one side of wave guide 2 with a choke groove ,4 cut in each which run parallel to the long narrow slot I.

As shown in Fig. 2, dimensions a (depth of choke groove) and b are about one-quarter guide wave-lengths at the operating frequency. choke 3 has the same efiect as. if a solid piece of The a, .441" b, .441" c, .625" Frequency, 9,375 megacycles Width of choke groove, .063"

. Clearance between choke and cylinder, .031"

Width of slot '1, .250"

If the embodiment of Fig. l were to be used without channel 5, then the total periphery of propagating opening 8 should be in the neighborhood of one'free space wave length.

Fig. 3 shows a cross-sectional view of Fig. 2 along" section line 3-3 showing the relation of the helical channel 5 and radiating aperture 8. It is to be noted that channel 5 is located the same distance from helical slot 6 at all points so that it always has the effect of shunting wave guide 2 with a low impedance no matter what the position of radiating aperture 8 may be. Besides having this shunting effect, it must be so placed as to provide a proper impedance termination in wave guide 2 in the vicinity of channel 5. One group of dimensions found satisfactory are as follows (refer to Fig. 3):

g=depth of helical channel=1.18 cin.

h=wide dimension of channel 5:.900"

i=distance of helical channel from propagating opening 8:.374"

5i=length of radiating aperture=1.'72 cm.

Width of radiating aperture=width of slot I (not shown in Fig. 3) =.25 0" (since helical angle=60 degrees, the peripheral width of radiating aperture was .250X1/sine 60 degrees=.288)

The length of narrow dimension of wave guide 2 (not shown in Fig. 3) =.400" v Since the helical angle was 60 degrees, the peripheral width m (see Fig. 6)v of radiating aperture frequency=9,375 megacycles The above dimensions are not critical and many variations can be made without deviating from the scope of the invention.

Of course, a circular wave guide could be substituted for rectangular wave guide 2.

Fig. 4 discloses another embodiment of the invention where the helical groove 6" is located on the wave guide and the straight slot 1'' is located on the cylinder. In order to place helical slot on a rectangular wave guide, the side of the wave guide containing the slot must be twisted to follow a helical surface. v

Since the radiating aperture 8 is to be moved along a straight line, the wave guide with the helical groove must be rotated. As previously explained, this embodiment is not very well adapted for use with a helical channel 5 such as found in the preferred embodiment of Fig. l.

Fig. 5 shows a third embodiment where :3, cylindrical wave guide 2" is used instead of a rectangular wave guide. Here again, the wave guide e a Iong, =narrowslot in -thewalf thereof a hollow 20 cylinder surrounding said wave guide-arid having its 'innenwall surface in contiguous relation to the wave guide wall forming the said slot, said noilow'cyii'rrder also having giangnarrow'siot in the wall ithereof.;t=nne.bf:.said slotsabeiiig relatively straight and the other slot following a helix-,hthe two slotsthereby overlappingl' to form a-radiating .-aperture, .a choke means extending ralon ithe 'z'sides ofl said wave guideslotlfor efiectively placing aslowimpedance across'th'finite gap'between the sides of said wave guide'slot and the contiguous inner surface of the cylinder, means coupled to the member containing the helical slot for rotating same thereby causing said radiatin aperture to traverse a straight line.

2. Electromagnetic propagating apparatus comprising in combination: a wave guide having a long, straight, narrow opening in its wall, a hollow cylinder surrounding said wave guide and havin its inner wall surface in contiguous relation to the portion of the wall of said wave guide which is adjacent said slot, said hollow cylinder having a helical slot in its wall whereby the said openings overlap to form a radiating aperture, a choke means extending alon the sides of said wave guide slot for effectively placing a low impedance across the finite gap between the sides of said wave guide slot and the contiguous inner surface of the cylinder, means coupled to said cylinder for rotating same thereby causing said- 50 radiating aperture to traverse a straight line.

3. Electromagnetic propagating apparatus comprisin in combination: a wave guide having a long, straight, narrow opening in its wall, a

hollow cylinder surrounding said wave guide and having its inner wall surface in contiguous relation to portion of the wall of said wave guide which is adjacent the said opening, said hollow cylinder having a substantially helical slot or opening in its wall whereby the said openings overlap to form a radiating aperture, and choke means extending along the sides of said wave guide slot for effectively placing a low impedance across the'finite gap between the sides of said wave guide slot and the contiguous inner surface of the cylinder.

4. Electromagnetic propagating apparatus comprising in combination: a wave guide having a long, narrow slot in its wall, a hollow cylinder surrounding said wave guide and having its inner wall surface in contiguous relation tothe wave guide wall forming the said slot, said hollow cylinder also having a long narrow slot in its Well, one of said slots being relatively straight and the other slot following substantially along ashelix,

wifating aperture rlappmgstolfornnazirael iokameansextending along tothiisides:csrsaia waveguide "slotforf ieffectively 5 pla 11 -narr s-l'o w 1; alhollow cylinder ding sa wave guide andhaving its inner relation to the. Wave id hollowcyleing reiativeiy straights and "or pening fol-lowing substantially we slots-thereby over-lapping apel-t i-e, adhoke means "pair of gro'o smembers extending th sides of said-wave 'gui-de slotgsaid along-she entire lengtn-oi said eing sue at a low impedance twee the sides-oi the waveguide-slot neccntiguous innersurface of the cylinder. apparatus narrow side, a hollew -eylinder surrounding said wave guide and having its inner wall surface in contiguous relation to the Wave guide wall forming the said slot, said hollow cylinder also having a long narrow slot in its wall, one of said slots or opening being relatively straight and the other slot or opening following substantially along a helix, the two slots thereby overlapping to form a radiating aperture, whereby rotation of the member containing the helical slot causes said radiating aperture to traverse a straight line and choke means extending along the sides of said wave guide slot for effectively placing a low impedance across the finite gap between the sides of said wave guide slot and the contiguous inner surface of the cylinder.

7. Electromagnetic propagating apparatus comprising in combination: a rectangular wave guide having a long, straight, narrow opening in its narrow side, a hollow cylinder surrounding said wave guide and having its inner Wall surface in contiguous relation to the portion of the wall of said wave guide which is adjacent the said opening, said hollow cylinder having a helical slot or opening in its wall whereby the said openings overlap to form a radiating aperture, means coupled to said cylinder for rotating same thereby causing said radiating aperture to traverse astraight line and choke means extending along the sides of said wave guide slot for effectively placing a low impedance across the finite gap between the sides of said wave guide slot and the contiguous inner surface of the cylinder.

8. Electromagnetic propagating apparatus comprising in combination: a wave guide having a long, straight, narrow opening in its wall, a hollow cylinder surrounding said wave guide and having its inner wall surface in contiguous relation to portion of the-wall of said wave guide which is adjacent the said opening, said hollow cylinder having a substantially helical slot or opening in its wall whereby the said openings overlap to form a radiating aperture, a helical channel formed on the inner surface of said cylpropagating apparatus tion to portion of the wall of said wave guide which is adjacent the said opening, said hollow cylinder having a substantially helical slot or opening in its wall whereby the said openings overlap to form a radiating aperture, means coupled to said cylinder for rotating same thereby-1 causing said radiating aperture totraverse a straight line, a first choke means comprising a pair of grooves members extending along both sides of said wave guide slot, said grooves extending alon the entirelength of said wave" guide slot and communicating withthe finite space between the sides of the wave guide adjacent the wave guide slot and the contiguous inner surface of the cylinder, the depth of the said grooves being such that a low impedance said cylinder and running parallel to the helical 0 slot of said cylinder, said channel being of such dimension that it reflects a low impedance across said wave guide on one side of the radiating aperture. 4

v 10. Electromagnetic propagating apparatus comprising in combination: a wave guide having a long, narrow slot in the wall thereof, ahollow cylinder surrounding said wave guide and having its inner wall surface in contiguousrelation to the wave guide wall forming the said slot, said hollow cylinder also having a long narrow slot in the wall thereof, one of said slots being relatively straight and the other slot following a helix, said helical slot making substantially a complete revolution, the two slots thereby overlapping to form a radiating aperture, means coupled to the member containing the helical slot for rotating same thereby causing said radiating aperture to traverse a straight line and choke means extending along the sides of said wave guide slot for efiectively placing a low impedance across the finite gap between the sides of said wave guide slot and the contiguous inner surface of the cylinder.

ALLEN S. DUNBAR. 

